持荷10年的钢筋钢纤维混凝土梁正常使用极限状态可靠度分析

Time-dependent reliability analysis of SFRC beams under sustained service loads of ten years

为分析持续荷载作用下钢筋钢纤维混凝土梁正常使用极限状态下可靠性的时变规律,基于持荷10 a的钢筋钢纤维混凝土梁抗弯试验结果,考虑随服役时间延长混凝土材料劣化、钢筋截面积削弱、钢筋和混凝土之间黏结系数降低和计算模式不定性系数等多因素影响机制,建立了基于裂缝宽度控制和挠度控制的时变可靠度分析模型。分别就持荷水平不变、钢纤维掺量改变和持荷水平改变、钢纤维掺量不变两组试件共10根梁,将等效抗力法和一次二阶矩法相结合,求得持荷10 a的钢筋钢纤维混凝土梁正常使用极限状态的时变可靠度指标。结果表明:钢纤维的掺入可有效抑制混凝土梁的裂缝宽度开展和挠度变形,未掺钢纤维梁的可靠指标明显低于掺入钢纤维梁的可靠指标。且钢纤维掺量越高,可靠度指标越大,裂缝宽度越小,挠度变形越小;持荷水平越小,梁的裂宽和挠度变形越小,基于裂缝宽度和基于挠度控制的可靠度指标均越大,且当持荷水平越接近,可靠度指标越接近,与试验结果吻合良好,可为钢筋钢纤维混凝土梁理论分析和设计提供参考。

To analyze the time-dependent reliability of steel fiber reinforced concrete( SFRC) beams under sustained service load,the deflection and crack width time-dependent reliability models based on ten years' bending tests data were established. The models take into account the degradation of concrete strength,the reduction of effective crosssectional dimensions,the decrease of bond coefficient between steel and concrete,and the time-dependency of uncertainty coefficients. Ten beams were divided into two series,one with a constant applied load while variable steel fiber content,and the other with the same steel fiber content but different applied loads. The time-dependent reliability indexes were calculated by the equivalent resistance method and the first-order second-moment method. The results show that the added steel fibers could restrain the crack width and deflection. The beam without steel fibers has a lower reliability index than the beam with fibers. The higher the steel fiber content or the smaller the applied load is,the larger the reliability index is,and the smaller the crack width and deflection are. In addition,the reliability indexes are almost the same with the similar applied loads. The results are compared with test data and show a good correlation.